Method of and means for providing a charge of water sensitive explosive in a blast hole



AITCHISON METHOD OF AND MEANS FOR PROVIDING A CHARGE OF WATER Nov. 20,1962 R. B.

SENSITIVE EXPLOSIVE IN A BLAST HOLE Filed Jan; 13, 1958 2. Sheets-Sheet1 L. iii v INVENTOR ROBERT B. AITCHISON ZTTORNE? 5, 8 14.44 Q a an i; I:F) 4 I I; iii! Evil I! I! If);

Nov. 20, 1962 R. B. AITCHISON METHOD OF AND MEANS FOR PROVIDING A CHARGEOF WATER SENSITIVE EXPLOSIVE IN A BLAST HOLE 2 Sheets-Sheet 2 R O T N EV m Filed Jan. 13, 1958 ROBERT B. AITCHISON BY V WW 3,064,572 PatentedNov. 26, 1962 3,064,572 METHOD OF AND MEANS FOR PROVIDING A CHARGE OFWATER SENSITIVE EXPLOSIVE IN A BLAST HGLE Robert B. Aitchison, New York,N.Y., assignor to Union Carbide Corporation, a corporation of New YorkFiled Jan. 13, 1958, Ser. No. 708,445 2 Ciaims. (Cl. 102-23) The presentinvention relates to a method of and means for providing a charge ofwater sensitive explosive in a blast hole, and more particularly to amethod of and means for charging a water-containing blast hole with awater sensitive explosive.

Blast holes are commonly prepared by air drilling or wet drillingmethods, and in some refractory formations of extreme hardness such asin taconite, for example, the hole is jet pierced by means of ahydrocarbon-oxygen high temperature flame. In some cases such holes havebeen prepared to depths greater than one hundred feet. The holes arecharged with conventional cartridges of explosive which are to bedetonated in the hole. Certain difliculties are often encountered whensuch methods are employed. Seepa-ge water has filled such holes tosubstantial depths; consequently expensive high grade water-proof packedexplosives have been used instead of inexpensive water sensitivecompounds such as ammonium nitrate and the like. Also, blast holes maybe de-watered but rain may completely ruin this work; likewise, any bagsof water sensitive explosives that might be stacked near the holes readyfor loading may be severely damaged from the standpoint of their use asa blasting agent.

Another disadvantage of the prior art blasting methods is that the wallsof the hole are quite often not perfectly regular and could cause atemporary jamming of the explosive cartridge in the hole therebypreventing their insertion to the bottom and forming an air pocketbeneath and around the cartridge. It is well known that such air pocketsproduce a cushioning eifect which decreases the blasting efiiciency.

One presently used method of charging such blast holes which partiallyovercomes the aforementioned problems involves the placement of a drillof an inexpensive water-sensitive explosive in a water-imperviousflexible plastic bag which is then lowered into the watercontainingblast hole for detonation. However, it has been found that such bags arefrequently punctured either from physical handling, contact withsharp-Wall surfaces within the hole, or by rock tremors from nearbyblasts. As a result, water seeps into the bag and at least partiallydissolves the water-sensitive explosive, thereby reducing itsefiectiveness as an explosive.

It is therefore an object of the present invention toprovide a method ofcharging water-containing blast holes with a water-sensitive explosivewhich does not lose its brisance value by virtue of such charging.

Another object is to provide a method of charging water-containing blastholes with a water sensitive explosive in such a manner that the contourof the hole has no efiect on the blasting efficiency.

A further object of the invention is to provide an explosive chargeincluding a granular water sensitive explosive which can be placed in awater-containing blast hole without loss of brisance value.

These and other objects and advantages of this invention will beapparent from the following description and accompanying drawings inwhich:

FIG. 1 is a side view, partly in cross section of a triple compositeplastic tubing assembly according to the present invention;

FIG. 2 is a view of a section of the inner tubing assembly portion ofFIG. 1, to be severed in preparing such assembly for insertion in theblast hole;

FIG. 3 is a view, partly in cross section, of the triple tubing assemblyof FIG. 1 after the outer tubing section has been pulled down andtransversely sealed;

FIG. 4 is a longitudinal sectional view of the triple tubing assemblytaken on line 4-4 of FIG. 3 with each of the tubes transversely sealedaccording to the present invention;

FIG. 5 is a longitudinal sectional view of the triple tubing assembly ofFIG. 4 after weighting material has been placed in the pocket at thelower end of the outer tube, and such pocket has been closed;

FIG. 6 is an elevational view of the triple tubing assembly of FIG. 5after such assembly has been longitudinally folded and banded togetherfor easy insertion into the blast hole;

FIG. 7 is a view of a longitudinal section through a blast hole intowhich the triple tubing assembly of FIG. 6 has been lowered and theintermediate tube inflated;

FIG. 8 is a similar view of the triple tube containing last hole of FIG.7 after the intermediate tube has been charged with an explosive mixtureof the present invention;

FIG. 9 is a similar view of the triple tube containing blasting hole ofFIG. 8 after the explosive mixturecontaining tube assembly has beenprimed, sealed, and stemmed;

FIG. 10 is a perspective view looking downwardly on a closure plug forthe upper ends of the intermediate and outer tubes;

FIG. 11 is a perspective view looking downwardly on a clamp which fitsaround the closure plug of FIG. 10 so as to secure the upper ends of theintermediate and outer tubes therebetween;

FIG. 12 is a perspective view looking downwardly on a stool assembly forsupporting the closure plug and clamp of FIGS. 10 and 11, respectively;and

FIG. 13 is a perspective view looking downwardly on a funnel which fitsinto the closure plug of FIG. 10 for charging the explosive mixture intothe intermediate tube.

In accordance with the method of the present invention, awater-sensitive explosive is charged in a blast hole by placing thereina hydrophobic explosive mixture encased within a water-imperviousflexible plastic coptainer, the mixture comprising the water-sensitiveexplosive, a liquid hydrocarbon, and a hydrophobic jelling material inan amount sufiicient to impart a jelly-like consistency to the liquidhydrocarbon. The jelling material acts as a water-proofing agent whichcoats the explosive, thus rendering the latter unaffected by accidentalleakage of water into the container.

The invention further provides a plastic tubing assembly from which theaforementioned container is formed, and a method of making such assemblyand preparing same for use, the tubing assembly including a relativelysmall diameter inner inflation tube longitudinally within a largediameter tube that is preferably double walled. A length of the tubingassembly is prepared for insertion in the blast hole by transverselysevering a section of the intermediate tube along with the correspondinginner tube section, and then transversely sealing the tubes below a gasexit notch of the inner tube. The section of the outer tube below theseal provides a pocket enclosure for a weighting material. The tubingassembly is preferably longitudinally folded for insertion in the blasthole and lowered therein, such assembly being sufliciently long for theupper ends of the tubes to extend out of the hole. Compressed gas isthen passed into the intermediate tube through the gas exit notch of theinner tube and the intermediate tube is inflated thereby to contact theblast hole walls. The aforementioned explosive mixture charge is nextintroduced into the inflated intermediate tube, followed by at least oneprimer. The upper end of the inflated intermediate tube is then closed,and the explosive charge is stemmed prior to detonation.

Referring more specifically to the drawings, FIGURE 1 illustrates atriple concentric lay-flat tubing assembly which is used in chargingblast holes according to the present invention. The assembly comprisesan inner inflation tube which is relatively thin walled, preferably witha thickness of between about 1 mil and 2 mils. The inner tube may havean inside diameter of about /2 to 1% inches, and a flattened width ofabout to 2 inches. About this tube is provided an intermediate flexibletube preferably having a wall thickness between about 2 mils and 3 mils,and an inside diameter of from 6% to 16 inches, or any diameter requiredby the diameter of the blast hole. The outer tube 22 preferably has awall thickness between about 2 mils and 3 mils, and an inside diameterlarge enough to enclose the intermediate tube 21. The tubes 20-22 areformed of flexible Water-impervious material, preferably a strongorganic plastic such as polyethylene, polyethylene terephthalate,polyvinylidene chloride, and the like, and can be seamless or made ofsheet material with longitudinal heat-sealed seams. This triple tubingassembly can be made up in standard lengths or in as long a length ascan be conveniently Wound on a reel for shipment and ease of handling.

FIGURES Q-6 illustrate the preferred method of preparing thetriple-tubing assembly for insertion in the blast hole. About 1 to 2feet of the end of the outer tubing 22 are transversely folded or turnedback on itself to expose a section 23 of the intermediate tube 21. Thissection along with the contained inner tube is transversely severedalong line 24, near the inner tube fold back, and discarded. Removal ofthe severed section 23 leaves an outer tube skirt 25 at the end of thetubing assembly. The unsevered inner tube 20 is then notched at points26 near the fold-back. A transverse seal 27 is then made across theinner and intermediate tubes 20 and 21, below the notching 26, at aboutthe severance point. Sealing may be accomplished by means well-known tothose skilled in the art, erg. by heat. This seals off the bottom of theintermediate tube 21 and temporarily anchors the inner tube 20 to theintermediate tube 21. The outer tube is now unfolded and a transverseseal 28 is made across this tube just below the sealing point of theintermediate tube, so as to form a pocket 29 from the skirt 25. Thismethod of construction preferably forms an intermediate tube bag 30within an outer tube bag 31, which provides greater insurance againstwater leakage into the explosive charge-containing intermediate bag 30,as described later in more detail. The tubes may alternatively be formedinto bags by gethering the ends as required, and tying such ends withstring or other fasteners. However, heat sealing is preferred when aheat scalable plastic is used because it insures a quickly obtained,inexpensive leaktight seal.

The pocket 29 is partly filled with weighting material 32 such as rockgranules or a soluble material as herein after described, and the excessskirt material is tied together by suitable means such as cord 33 toform bag-like enclosure 29a. The latter is also preferably tied off at apoint near or just below the seals 27 and 28. The cord 34 used for thistie off may be left with one or two ends 35 long enough to extend thefull length of the tubing assembly needed for the full depth of the borehole. Such cords can be used to lower the weighting materialcontainingtubing assembly into the bore hole so as to lessen the strain on theplastic tubes.

The composite tubing assembly is next preferably longitudinally foldedseveral times as shown in FIGURE 6 to provide a narrow width of finalassembly which is readily lowered into a bore hole without excessivecontact with the rough surface of the hole walls. Such folds 36 can beretained by applying bands of paper 36a around the folded assembly or byuse of small pieces of pressure sensitive tape, or by the application ofa small quantity of suitable adhesive between folds, any of which isreleased by a slight pressure.

To load or charge a blast hole containing water, it is preferable tolimit the amount of water present to no more than about 3 to 5 feetdepth from the bottom, and to remove any excess of water by, forexample, pumping. If desired, a suitable quantity of water may be pouredinto an irregularly shaped dry hole to avoid an air baffle whichinterferes with the shock waves of the blast.

Referring now to FIGURES 7 through 13 which illustrate the method andapparatus for loading or charging a blast hole with a Water-sensitiveexplosive, the folded tubing assembly of FIGURE 6 is lowered with theaid of cords 35 until the Weighted bag-like enclosure 29a restspreferably on the bottom of the hole, or seeks its natural level belowthe surface of the water. The upper edges of intermediate and outertubes are then pulled around closure plug 37 and pressed against suchplug by adjustable ring clamp 38 which is preferably mounted on legs 39as a stool 4th. The inner tube 20 is connected through a small diameterhole 4-1 in closure plug 37 to a source of pressurized gas, such as air(not illustrated). A charging funnel 42 fits in a larger diameter hole43 in the closure plug 37, and communicates with a hopper containing theexplosive charge (not illustrated). A pressure relief valve 44communicates with and closes another small diameter hole 45 in closureplug 37. it will be apparent from the foregoing description that theupper ends of the intermediate and outer tubes are separated from theatmosphere.

Compressed gas, e.g., air, is now blown in through inner tube 20 andthis air escapes through notches 26 at the lower end thereof into theintermediate tube at a point near the lowest part of the region oftubing assembly which is pressed together by water pressure. This willcause the tubes to be inflated evenly. The paper bands or other mediumemployed for holding the tubing assembly in the folded condition areeasily burst by the air pressure.

When the tubing is inflated so that the outer tube 22 is in substantialcontact with the hole Walls, including the walls of any enlarged orchambered portions 46 which may exist, the prepared free flowingexplosive charge 47 may be introduced by opening the valve at the bottomof the hopper device. Such charging may be facilitated by applyingregulated air pressure to the upper part of the hopper, andover-pressurizing the plastic tubing is avoided by the presence ofrelief valve 44 which is set to open at the desired maximum pressure inthe inflated intermediate tube 21.

When the hole has been partially charged with the hydrophobic explosivemixture 47, the closure plug 37 may be removed for the insertion of thefirst primer cartridge 48 at an intermediate level above the bottom ofthe tubing assembly. After the first primer has been lowered to itsproper place, the latter may, for example, be fused with Prima-cords 49which may be set in notches 50 provided in closure plug 37. Next, theinner tube 29 may be removed if desired by simply pulling it out, as itwill tear off at the notches 26 which were provided just above thetransverse seals 27. After the remainder of the explosive and one ormore additional primers have been charged, the upper part of theintermediate and outer tubes 21 and 22 may be tied off and the remainderof the hole stemmed in a manner wellknown to those skilled in the art,as illustrated in FIGURE 9.

An important aspect in this invention is the provision of a surplus oftubing assembly length ie at least a 50-foot length of tubing willnormally be required for a 45-foot depth hole. This is because the bagconforms to the irregularities of the hole wall to a very substantialdegree, as the free flowing explosive charge falls into the bag. Whereno surplus of tubing length is provided, the strain of such conformingmight cause rupture of the bags.

One advantage of the present invention is that even though the outerplastic tube 22 might be torn or punctured during the charging step, theintermediate tube 21 will continue to be an effective moisture barrier.Thus, with the upper end of the tubes tied off, a charged hole can beleft for an extended period before the blasting date. This allowssufiicient time for successive loading of many holes so as to make up alarge and economical blast, and without the danger of moisturepenetrating the explosive charge to a degree that would reduce theexplosiveness of such charge.

While the previously described method of charging blast holes makes itpractical to employ a low cost watersensitive explosive such as ammoniumnitrate, it is advisable to avoid the moisture difliculties which wouldoccur if the untreated explosive were used and both the intermediate andouter plastic bags should become ruptured or otherwise damagedespecially near the bottom of the hole.

It has been found that the explosive efficiency of ammonium nitrate inthe form of prill can substantially be increased by the addition of aliquid hydrocarbon. Its effectiveness is also increased by treatmentwith other relatively non-compressible materials. Treatment withhydrocarbon liquid such as kerosene or fuel oils will reduce theammonium nitrates sensitivity to water to a certain degree but notsufliciently for present purposes.

The water resistance of low cost, water sensitive explosives can begreatly increased by incorporating a hydrophobic jelling agent in thehydrocarbon liquid to be mixed with the granular explosive. Metallicsoaps have been found suitable as jelling agents. For example, in onetest kerosene was employed as the hydrocarbon liquid and to this wasadded an aluminum soap of 2- ethylhexoic acid compound in the proportionof 7 parts, by weight, of the soap to 100 parts of kerosene. The soapwas completely dissolved in the kerosene by stirring and heating toabout 125 to 150 F., and after cooling the liquid acquired a jelly-likeconsistency. Ammonium nitrate prill was then added to form a freelyfiowable slurry. The proportions were about 1 gallon of the solution toabout 80 lbs. of commercial-grade ammonium nitrate. The increased waterresistance attain able by the present invention was shown experimentallyby stirring ammonium nitrate with the jelly-like hydrocarbon mixture,draining off the excess liquid, and placing the otherwise unprotectedaluminum nitrate in a cold water bath. It was readily apparent that thehydrophobicly jelled hydrocarbon coated the ammonium nitrate granuleswith a protective film, and only after 35 minutes was there anyappreciable dissolving action of the water on the ammonium nitrate. Thiscompares favorably with a similar test in which uncoated ammoniumnitrate was placed in cold water and found to dissolve immediately, anda third test in which ammonium nitrate was coated with untreatedkerosene, placed in cold water, and found to dissolve in less than 2minutes.

Thus, the hydrophobicly jelled kerosene protective film was found to bestable when immersed in water for relatively long periods, and wasbroken during the interim only by stirring. When the jelled keroseneammonium nitrate mixture is charged into the plastic bag in a bore hole,only a very small area of the mixture adjacent a possible puncture ofthe intermediate tube bag can be subject to the action of Water in thebore hole. The dissolving action of the water is so greatly retardedthat only a very small portion of the explosive can be inactivated inperiods substantially longer than M. hour.

When aluminum soaps are employed with hydrocarbons of the kerosene type,it is found that about 3% by weight of the soap is sufficient to imparta jelly-like consistency to the liquid with 7% the preferred upperlimit, although up to about 10% by weight aluminum soap can be used.Other suitable liquid hydrocarbons suitable for practice of the presentinvention include gasoline, kerosene, and fuel oil. Also, otherwell-known jelling agents that are hydrophobic may be used, such ascolloidal carbon blacks, colloidal silicas, and mineral waxes. Thehydrocarbon-jelling agent mixture should form at least about 10% byweight of the explosive.

It is important that the charge fill the blast portion of the hole ascompletely as possible, so as to avoid air pockets which tend to cushionthe explosion and decrease the explosive efficiency. To this end, it ispreferable to employ a weighting material having a high bulk density andwhich is comminuted fine enough to spread out against the bottom of theblast hole so as to avoid air spaces. Since water in the blast holecontributes to fill any spaces as a non-compressible shock transmittingmedium, it will be advantageous to puncture the weight material bag sothat water can mix with the comminuted weighting material and fillspaces between the individual particles. Alternatively, it is alsocontemplated that the comminuted weighting material may consist of watersoluble substance such as a metal salt which, when water leaks throughsuit-ably sized small punctures, will dissolve slowly to allow theexplosive charge above it to sink and fill the bottom of the blast holemore snugly and completely with active explosive. In this waypractically no loss in blast hole depth is sustained.

Although preferred embodiments of the invention have been described indetail, it is contemplated that modifications of the method, apparatus,and explosive mixture may be made and that some features may be employedwithout others, all within the spirit and scope of the invention. Forexample, when a jelled hydrocarbon ammonium nitrate mixture is employed,it has been found that the water resistance of the water-sensitiveexplosive is so improved that instead of a triple tubing assembly, adouble tubing assembly can be employed. Also, in a dry blast hole oreven when only a small amount of water is present, the jelledhydrocarbon treated explosive can be charged directly into the holewithout the use of plastic bags.

What is claimed is:

1. A method of preparing for insertion in a blast hole, a length offlexible thin-walled plastic triple tubing assembly comprising an innertube, an intermediate tube concentric to and surrounding said inner tubewith an annular space therebetween, and an outer tube concentric to andsurrounding said intermediate tube, which method comprises transverselyfolding back on itself a desired length of said outer tube therebyexposing a section of said intermediate tube, transversely severing theexposed intermediate tube section along with the corresponding enclosedinner tube section at a point near the outer tube fold-back, notchingthe unsevered inner tube near the fold-back, transversely sealing theintermediate and inner tubes below the notching at about the severancepoint, unfolding the outer tube and transversely sealing such tube belowthe first seal so as to form a pocket, placing in said pocket below theouter tube seal a desired amount of granular weighting material, closingoff the lower end of said outer tube to form a bag-like enclosure fromsaid pocket to retain the weighting material, and longitudinally foldingthe triple tube assembly for insertion in the blast hole.

2. A method of blasting by means of a water-sensitive explosive in awater containing blast hole which comprises providing a length offlexible thin-walled plastic triple tubing assembly comprising an innertube, an intermediate tube concentric to and surrounding said inner tubewith an annular space therebetween, and an outer tube concentric to andsurrounding said intermediate tube; preparing said length for insertionin the blast hole by transversely fold- 3,oea,572

7 ing back on itself a desired length of said outer tube therebyexposing a section of said intermediate tube, laterally severing theexposed intermediate tube section along with the corresponding enclosedinner tube section at a point near the outer tube fold-back, partiallynotching the unsevered inner tube near the fold-back, transverselysealing the intermediate and inner tubes below the notch ing at aboutthe severance point, unfolding the outer tube and transversely sealingsuch tube 'below the first seal so as to form a pocket, placing in saidpocket below the outer tube seal a desired amount of granular weightingmaterial, closing off the lowerend of said outer tube to form a bag-likeenclosure from said pocket to retain the weighting material, andlongitudinally folding the triple tube assembly for insertion in theblast hole; lowering the longitudinally folded triple tube assembly intothe blast hole; separating the upper end of said intermediate tube fromthe atmosphere and passing compressed gas into said inner tube andthrough said notching into said intermediate tube so as to inflate saidintermediate and outer tubes sufficiently to contact the blast holewalls; providing a freely flowing hydrophobic explosive chargecomprising said water-sensitive explosive coated with a hydrophobiclyjelled hydrocarbon liquid; introducing the explosive charge into theinflated intermediate tube; introducing at least one primer into suchinflated tube; closing the upper portion of the inflated intermediatetube; stemming the explosive charge and detonating such charge.

References Cited in the file of this patent UNITED STATES PATENTS2,069,612 Kirst et a1 Feb. 2, 1937 2,687,093 Botts Aug. 24, 19542,703,528 Lee et al Mar. 8, 1955 2,704,514 Barlow et al Mar. 22, 19552,733,658 Moat Feb. 7, 1956 2,745,346 Aitchison et a1 May 15, 19562,751,283 Van Strien et al June 19, 1956 2,772,632 Aitchison et a1. Dec.4, 1956 2,814,555 Rinkenbach et a1 Nov. 26, 1957 2,817,581 Rinkenbach eta1 Dec. 24, 1957 2,818,809 Roy Jan. 7, 1958 2,835,197 Ferguson May 20,1958 2,903,969 Kolbe Sept. 15, 1959 2,911,910 Welsh Nov. 10, 1959FOREIGN PATENTS 5,222 Great Britain 1886

